Modern wireless communications systems place great demands on the antennas used to transmit and receive signals. Antennas may be required to produce a radiation pattern with a carefully tailored and well defined beamwidth in azimuth and elevation, while maintaining high gain characteristics and operating over a broad bandwidth. In particular in a fixed wireless access system, in which customer premises equipment may be installed at a determined orientation for communication with a base station, it may be required that antennas produce a radiation pattern that has well defined directional characteristics to reduce path loss to the base station and to minimise interference to neighbouring systems, and that produces a beam with a predictable orientation with respect to the antenna structure in order to facilitate the installation of the equipment. In addition, the antenna is typically required to have a low cost of manufacture and a small size.
A patch antenna is a type of antenna that may typically be used in a wireless communications system, for example at a base station or at a user equipment terminal, such as customer premises equipment. A patch antenna typically comprises a sheet of metal known as a patch radiator, disposed in a substantially parallel relationship to a ground plane. There may be a dielectric material between the patch radiator and the ground plane, such as a typical printed circuit board substrate comprising, for example, a composite of glass fibre and resin, or there may be an air dielectric, in which case the patch radiator may be held in position in relation to the ground plane by non-conducting spacers, for example. The patch radiator may be, for example, rectangular with one side of approximately half a wavelength in length at an operating frequency of the antenna, and is typically connected to a radio transceiver by a feed track of defined characteristic impedance, typically 50 Ohms. The feed track typically connects to the patch antenna at a feed point adjacent to an edge of the patch radiator, or at a point recessed into the patch for improved impedance matching, and the feed track is typically formed in the same plane as the patch radiator. For example, the feed track and patch radiator may be formed as etched copper areas on one side of a printed circuit board, and the ground plane may be formed on the other side.
However, typical patch antennas may have a radiation pattern that shows asymmetry and may form a beam that is offset in direction from a desired direction normal to the ground plane, in particular when used with a ground plane of limited size. In addition, gain and bandwidth of the antenna may be limited.
It is an object of the invention to mitigate the problems of the prior art.